Anti-listeria bacteriocin

ABSTRACT

The invention concerns an isolated polypeptide which is a bacteriocin called Sakacine G derived from  Lactobacillus sakei  2512. The invention also concerns a nucleic acid coding for said bacteriocin and the use of said polypeptide as active agent against pathogenic and undesirable flora in the preparation of food products.

[0001] The present invention relates to a bacteriocin of Lactobacillus sakei and more especially of Lactobacillus sakei 2512, to a nucleotide sequence coding for that bacteriocin, and to the industrial use of that bacteriocin as an active agent against pathogenic or undesirable flora in the preparation of food products.

[0002] Lactic acid bacteria are used intensively in the fermentation of foods not only to improve the taste and texture of the foods but especially to prolong their storage life. Numerous lactic acid bacteria are in fact capable of inhibiting the growth of certain Gram positive bacteria, including pathogenic strains such as Listeria monocytogenes, thanks to the excretion of antagonistic molecules, including peptide compounds. These peptide compounds, called bacteriocins, are therefore potentially valuable for preserving fermented food products in terms of quality and health.

[0003] As examples of such bacteriocins, special mention may be made of those which form the sub-class of polypeptides called anti-Listeria bacteriocins, bacteriocins of class IIa (Ennahar S. et al., 2000, FEMS Microbiol. Rev., 24: 85-106) and cystibiotic bacteriocins (Jack R. et al., 1995, Microbiol. Rev., 59(2): 171-200). The potential use of one of these class IIa bacteriocins, divercin V41, for preventing the growth of Listeria monocytogenes in smoked salmon has recently been noted (Duffes F. et al., 1999, J. Food Prot., 62(12): 1394-1403).

[0004] The sequences of these polypeptides exhibit strong similarities in the N-terminal portions, with the presence of a disulfide bridge in particular. The hydrophobic C-terminal portion is much more variable, but some of those bacteriocins, so-called pediocin-type bacteriocins (pediocin PA-1, enterocin A and divercin V41), are characterised by a number of residues greater than 40 and the presence of a second disulfide bridge on the C-terminal side.

[0005] The authors of the present invention have discovered a new class IIa bacteriocin produced from a specific strain of Lactobacillus sakei, which proves to be especially effective in inhibiting the growth of Listeria, more especially of Listeria monocytogenes.

[0006] In agreement with Tagg J. R. et al., Bacteriol. Rev., 40: 722-756 (1976), the term “bacteriocin” within the scope of the invention refers to a polypeptide produced, by ribosome synthesis, from microorganisms capable of inhibiting specifically the growth of other bacteria.

[0007] The present invention therefore relates in the first instance to a polypeptide derived from the strain Lactobacillus sakei 2512, having bacteriocin activity.

[0008] The strain Lactobacillus sakei 2512 was deposited on 25th May 2000 with the Collection Nationale des Cultures de Microorganismes (National Collection of Microorganism Cultures), where it is registered under deposit number 1-2479.

[0009] The bacteriocin to which the present invention relates has been named sakacin G. It is a polypeptide having a molecular mass of the order of from 3700 to 3900 and preferably of about 3834 Da, determined by mass spectrometry. It has a bacterial inhibition spectrum which is very similar to that of the class IIa bacteriocins. Accordingly, it proves to be especially effective against the strains of Lactobacillus sakei other than Lactobacillus sakei 2512, Pediococcus cerevisiae, the totality of the Listeria strains and against Enterococcus faecalis and Enterococcus durans. By contrast, it proves to be inactive against the other species of Lactobacillus such as, for example, Lactobacillus debrueckii, Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus casei and a strain of Enterococcus faecium.

[0010] Like the anti-Listeria bacteriocins of the pediocin type, sakacin G advantageously possesses two disulfide bridges in its peptide structure.

[0011] An analysis of the genetic determinants of several class IIa bacteriocins has shown that the genes involved in their production, transport and immunity are organised into one or more operon-type structures. These operons are often located in a plasmid and generally possess at least two genes coding for proteins, homologous to an ABC transporter and an accessory protein, probably involved in bacteriocin export.

[0012] Cloning of the nucleotide fragment containing the sakacin G gene has revealed the existence of three complete open reading frames skgA1 (SEQ ID No. 1), skgA2 (SEQ ID No. 3) and skgDc (SEQ ID No. 13) (including the truncated reading frame skgD (SEQ ID No. 7)) and a truncated frame skgI (SEQ ID No. 5), a diagrammatic representation of which is shown in FIG. 1. The nucleotide fragment is a double strand, the 5′-3′ single strand of which is shown in sequence ID No. 15.

[0013] The products of the genes skgA1 and skgA2, called pre-bacteriocins, may undergo maturation during which their respective leader peptides are cleaved between residues 18 and 19, thus liberating active sakacin G (residues 19-55).

[0014] The 5′-3′ single-strand nucleotide fragment comprising skgA1, skgA2, skgD and skgI appears in SEQ ID No. 9.

[0015] The present invention accordingly relates also to an isolated polypeptide corresponding to a bacteriocin, characterised in that it comprises sequence ID No. 2 and/or sequence ID No. 4. The sequence of the mature bacteriocin corresponds to sequence ID No. 12 and is comprised in sequences ID No. 2 and ID No. 4.

[0016] The reading frame called skgI codes for a protein of 52 residues. A comparison of that sequence with the database sequence shows strong similarities between SkgI and so-called immunity proteins. It probably codes for the immunity protein protecting the sakacin-G-producing bacterium.

[0017] The present invention extends also to an isolated polypeptide comprising sequence ID No. 6 corresponding to the reading frame skgI.

[0018] With regard to the last gene skgDc, it codes for a protein which is homologous with proteins of the ABC transporter family, and more especially of the transporter of pediocin PA-1. The gene skgDc probably codes for the ABC transporter specific to sakacin G.

[0019] The present invention extends also to the isolated polypeptide comprising sequence ID No. 8 corresponding to the so-called skgD gene, and to the isolated polypeptide comprising sequence ID No. 14 corresponding to the so-called skgDc gene.

[0020] It will be understood that homologous sequences are also included, which sequences are defined as

[0021] i) sequences that are similar to at least 70% of sequence SEQ ID No. 2, No. 4, No. 6, No. 8, No. 12 or No. 14; or

[0022] ii) sequences coded for by a homologous nucleic acid sequence as defined hereinbelow, that is to say a nucleic acid sequence that hybridises with sequence SEQ ID No. 1, No. 3, No. 5, No. 7, No. 9, No. 13 or No. 15 or its complementary sequence, under stringent hybridisation conditions.

[0023] There too, the term “similar” refers to perfect resemblance or identity between the amino acids of the homologous sequences under comparison, but also to non-perfect resemblance, which is referred to as similarity. This search for similarities in a polypeptide sequence takes into account conservative substitutions, which are substitutions of amino acids of the same class, such as substitutions of amino acids in non-charged side chains (such as asparagine, glutamine, serine, threonine and tyrosine), of amino acids in basic side chains (such as lysine, arginine, histidine), of amino acids in acid side chains (such as aspartic acid and glutamic acid); of amino acids in non-polar side chains (such as glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan and cysteine).

[0024] More generally, therefore, “homologous amino acid sequence” is understood as being any amino acid sequence that differs from sequence SEQ ID No. 2, No. 4, No. 6, No. 8, No. 12 or No. 14 by substitution, deletion and/or insertion of an amino acid or of a reduced number of amino acids, especially by substitution of natural amino acids by non-natural amino acids or pseudo-amino acids in positions such that these modifications do not significantly affect the biological activity of the isolated polypeptide and preferably of sakacin G.

[0025] Such a homologous amino acid sequence is preferably similar to at least 85% of sequence SEQ ID No. 2, No. 4, No. 6, No. 8, No. 12 or No. 14, preferably at least 95%.

[0026] Homology is generally determined using sequence analysis software (for example Sequence Analysis Software Package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison, Wis. 53705). Similar amino acid sequences are aligned in order to obtain the maximum degree of homology (i.e. identity or similarity, as defined above). To that end, it may be necessary to introduce gaps into the sequence artificially. Once optimum alignment has been achieved, the degree of homology is established by recording all the positions in which the amino acids of the two sequences under comparison are identical, relative to the total number of positions.

[0027] The biological activity of the isolated polypeptide, and especially of sakacin G, refers to its capacity to inhibit the growth of undesirable and/or pathogenic bacterial strains, preferably of Listeria bacteria and more especially of Listeria monocytogenes bacteria.

[0028] The present invention relates also to an isolated nucleic acid coding for a polypeptide as defined above.

[0029] More precisely, the present invention relates to an isolated nucleic acid comprising sequence ID No. 1 and/or sequence ID No. 3.

[0030] The complete nucleotide sequence of the region involved in the expression of sakacin G (3055 bp) has been determined. It is a double-strand DNA whose 5′-3′ strand is shown in sequence ID No. 15. The 3′-5′ strand is shown in FIG. 2. The present invention relates also to a nucleic acid comprising such a sequence.

[0031] As described above, this sequence has three complete open reading frames skgA1, skgA2 and skgDc and a truncated frame skgI. The supposed genes skgA1 (SEQ ID No. 1), skgA2 (SEQ ID No. 3) and skgI (SEQ ID No. 5) are oriented therein in the opposite direction relative to skgDc (SEQ ID No. 13).

[0032] Within the scope of the present invention there are also claimed the nucleic acid comprising sequence ID No. 5, the nucleic acid comprising sequence ID No. 13 and the nucleic acid comprising sequence ID No. 7.

[0033] It will be understood that homologous sequences are also included, which sequences are defined as:

[0034] i) sequences that are similar to at least 70% of sequence SEQ ID No.1, No. 3, No. 5, No. 7,No. 9,No.13 or No. 15; or

[0035] ii) sequences that hybridise with sequence SEQ ID No. 1, No. 3, No. 5, No. 7, No. 9, No. 13 or No. 15 or their complementary sequence, under stringent hybridisation conditions; or

[0036] iii) sequences coding for the polypeptide named sakacin G, as defined above.

[0037] A homologous nucleotide sequence according to the invention is preferably similar to at least 75% of the sequence SEQ ID No. 1, No. 3, No. 5, No. 7, No. 19, No. 13 or No. 15, preferably at least 85% or at least 90%.

[0038] Such a homologous nucleotide sequence preferably hybridises specifically with the complementary sequences of sequence SEQ ID No. 1, No. 3, No. 5, No. 7, No. 9, No. 13 or No. 15 under stringent conditions. The parameters defining the stringency conditions depend on the temperature at which 50% of the coupled strands separate (Tm).

[0039] For sequences comprising more than 30 bases, Tm is defined by the equation (Sambrook et al., 1989, NY: Cold Spring Harbor Laboratory):

Tm=81.5 +0.41(% G+C)+16.6 Log(cation concentration)−0.63(% formamide)−(600/number of bases)

[0040] For sequences having a length less than 30 bases, Tm is defined by the equation:

i Tm=4(G+C)+2 (A+T).

[0041] Under appropriate stringency conditions, under which the aspecific sequences do not hybridise, the hybridisation temperature may preferably be from 5 to 10° C. below Tm, and the hybridisation buffers used are preferably solutions of high ionic strength, such as a 6×SSC solution, for example.

[0042] The expression “similar sequences” used above refers to perfect resemblance or identity between the nucleotides under comparison, but also to non-perfect resemblance, which is referred to as similarity. This search for similarities in nucleic sequences distinguishes, for example, purines and pyrimidines.

[0043] A homologous nucleotide sequence having the open reading frames shown in SEQ ID No. 1, No. 3, No. 5, No. 7, No. 9, No. 13 or No. 15 therefore includes any nucleotide sequence which differs from sequence SEQ ID No. 1, No. 3, No. 5, No. 7, No. 9, No. 13 or No. 15 by mutation, insertion, deletion or substitution of one or more bases, or by the degeneracy of the genetic code, insofar as it codes for a polypeptide having the biological activity of sakacin G, as defined hereinbelow.

[0044] Such homologous sequences include sequences of the genes of bacteria other than Lactobacillus, coding for sakacin G.

[0045] The polypeptides of the present invention can be synthesised by any method known to the person skilled in the art. The polypeptides of the invention may, for example, be synthesised by techniques of the chemistry of synthesis, such as Merrifield-type synthesis, which is advantageous for reasons of purity, of antigen specificity, of the absence of undesirable secondary products and of ease of production.

[0046] The present invention relates also to a process for the production of a recombinant polypeptide, in which a vector comprising a nucleic acid according to the present invention is transferred into a host cell which is cultured under conditions permitting the expression of a polypeptide according to the present invention or of a polypeptide coded for by a nucleic acid sequence according to the present invention.

[0047] The recombinant bacteriocin may also be produced by a process in which a vector containing a nucleic acid comprising a nucleotide sequence according to the invention, and preferably the sequences SEQ ID No. 1 and/or No. 3 or a homologous sequence, is transferred into a host cell which is cultured under conditions permitting the expression of the corresponding polypeptide. The resulting protein can then be recovered and purified. The purification processes used are known to the person skilled in the art. The resulting recombinant polypeptide can be purified starting from lysates and cell extracts, from the supernatant of the culture medium, by methods used individually or in combination, such as fractionation, methods of chromatography, techniques of immunoaffinity with the aid of specific monoclonal or polyclonal antibodies, etc.

[0048] The nucleic acid sequence of interest, coding for sakacin G, can be inserted into an expression vector in which it is linked in an operative manner to elements permitting regulation of its expression, such as, especially, promoters, activators and/or transcription terminators. The signals controlling the expression of the nucleotide sequences (promoters, activators, termination sequences, etc.) are chosen depending on the cell host used. To that end, the nucleotide sequences according to the invention can be inserted into vectors which replicate autonomously within the chosen host, or vectors which integrate in the chosen host. Such vectors will be prepared by the methods conventionally used by the person skilled in the art, and the clones resulting therefrom can be introduced into a suitable host by standard methods, such as, for example, electroporation or calcium phosphate precipitation.

[0049] The cloning and/or expression vectors as described above, containing a nucleotide sequence defined according to the invention, also form part of the present invention.

[0050] The invention relates also to the host cells transformed, temporarily or permanently, by those expression vectors. These cells can be obtained by introducing into host cells, preferably prokaryotic host cells, a nucleotide sequence inserted into a vector as defined above, then culturing said cells under conditions permitting the replication and/or expression of the transferred nucleotide sequence.

[0051] Examples of host cells include especially bacteria such as Lactococcus, Lactobacillus, Leuconostoc, Streptococcus, Pediococcus, Escherichia and yeasts.

[0052] The nucleotide sequences of the invention may be of synthetic or natural origin. They may be DNA or RNA sequences obtained by the screening of sequence libraries by means of probes produced on the basis of the sequences SEQ ID No. 1, No. 3, No. 5, No. 7, No. 9, No. 13 and/or No. 15. Such libraries can be prepared by conventional techniques of molecular biology known to the person skilled in the art.

[0053] The nucleotide sequences according to the invention can also be prepared by chemical synthesis, or alternatively by mixed methods including the chemical or enzymatic modification of sequences obtained by the screening of libraries.

[0054] The present invention relates also to a method of inhibiting the growth of Listeria, more especially of Listeria monocytogenes, in an environment which may or may not be a food environment and which is susceptible to contamination by Listeria monocytogenes.

[0055]Listeria monocytogenes are pathogenic microorganisms which are the source of severe diseases in humans and animals and which especially can easily be transmitted by contaminated foods, more especially by means of meat, meat products, seafood products, milk and products derived therefrom. The present invention therefore proposes a method of inhibiting the growth of Listeria monocytogenes in a food likely to contain Listeria monocytogenes as a contaminant, said process comprising the addition of a polypeptide according to the invention to said food in an amount sufficient to inhibit the growth of Listeria monocytogenes.

[0056] The bacteriocins according to the invention are preferably used in any food system in an amount of from 1 to 100,000 arbitrary units (AU) of bacteriocins per gram of food.

[0057] An AU of bacteriocins is defined as 5 μl of the highest dilution of the culture supernatant leading to a defined growth inhibition zone, relative to a control strain of a Gram positive bacteria, on an agar medium.

[0058] Although foods are most affected by Listeria monocytogenes contamination, veterinary and medical products can also be contaminated with this type of bacteria, as can cosmetic products or similar products.

[0059] The bacteriocins according to the present invention, and especially sakacin G, can therefore also be used to inhibit the growth of this type of pathogen in such products.

[0060] Accordingly, the present invention relates to the use of a bacteriocin according to the present invention as an active agent against pathogenic or undesirable flora, especially in the preparation of food products, and more precisely to inhibit the growth and propagation of Listeria, more especially of Listeria monocytogenes, in food products.

[0061] The polypeptide can be incorporated as such into the food product in question, or alternatively it can be produced therein from the strain Lactobacillus sakei 2512.

[0062] Accordingly, the present invention relates also to the use of the strain Lactobacillus sakei 2512 in a food product to generate therein a bacteriocin polypeptide according to the invention.

[0063] The invention relates also to a bacteriocin composition, characterised in that it comprises at least one polypeptide according to the present invention, that is to say derived from the strain Lactobacillus sakei 2512 or comprising sequence SEQ ID No. 2 or No. 4 or No. 12 or No. 14 or the strain Lactobacillus sakei 2512.

[0064] The invention extends also to the use of the strain Lactobacillus sakei 2512 intended to produce a polypeptide as defined above, for inhibiting the growth and propagation of Listeria, more especially of Listeria monocytogenes, in food products, and the compositions comprising that strain.

[0065] The Examples and the Figure below are given by way of example and do not limit the subject-matter of the present invention.

FIGURE

[0066]FIG. 1: Diagrammatic representation of the genetic locus involved in the production of sakacin G.

[0067]FIG. 2: Complementary 3′-5′ strand corresponding to the complete nucleotide sequence of the region involved in the expression of sakacin G and the 5′-3′ strand of which is shown in SEQ ID No. 15.

MATERIALS AND METHODS

[0068] Bacterial strains and culture media. Lactobacillus sakei 2512 is cultured at 30° C. in MRS medium (DIFCO Laboratories) sterilised for 12 minutes at 110° C. The indicator strains are cultured in BHI medium (brain-heart infusion; DIFCO Laboratories) at 37° C.

[0069] Test of activity. BHI medium, supplemented with 10 g/l agar, is inoculated at 1% with a preculture of the indicator strain in stationary phase before being poured into a Petri dish. 50 microlitres of sakacin G solution are placed in wells formed in cooled agar with a hole punch. The bacteriocin activity manifests itself in the appearance of inhibition zones around the wells after incubation overnight at 37° C.

[0070] Protein analysis. Sakacin G is analysed by mass spectrometry using a Perkin-Elmer Sciex API 165 device equipped with an Ionspray ionisation source. After lyophilisation, the active HPLC fraction is taken up in an acetonitrile/water solution (1:1) containing 0.1% formic acid, and then injected by infuision at a rate of 5 μl/minute.

[0071] The protein concentration is determined by the bicinchoninic acid method by means of the BCA kit (Sigma) according to the manufacturer's instructions.

[0072] Protein sequence comparisons are carried out using the BLAST (1) program, obtainable from the ExPASy server of the Swiss Institute of Bioinformatics.

[0073] Molecular cloning and transformation. The plasmids are extracted and purified from strains of Escherichia coli and Lactobacillus sakei 2512 according to the methods previously described by Sambrook et al., 1989, NY: Cold Spring Harbor Laboratory and Muriana and Klaenhammer, 1987, Appl. Environ. Microbiol., 53: 553-560, respectively.

[0074] The DNA restriction and modification enzymes are used according to the supplier's instructions (Gibco-BRL). Analytical and preparative agarose gel electrophoreses are carried out in Tris/borate/EDTA buffer (pH 8.3) according to the methods described by Sambrook et al., 1989, NY: Cold Spring Harbor Laboratory. The digested DNA fragments are purified starting from agarose gels using the “Prep-a-Gene” kit (Bio-Rad). Cloning in plasmids pGEM-T (Promega) and pZERO2 (Invitrogen) is carried out in accordance with the suppliers' recommendations. Southern-type transfer is carried out on nylon membrane (Hybond-N+, Amersham) according to Sambrook et al., 1989, NY: Cold Spring Harbor Laboratory. The transfer is followed by hybridisation using a radioactive probe obtained by ³²p labelling with the aid of a “random primers DNA labelling system” kit (Gibco-BRL). The E. coli bacteria are rendered competent and transformed according to the method of Hanahan, 1983, J. Mol. Biol. 166: 557-580.

[0075] Taq polymerase (Gibco-BRL) is used according to the supplier's recommendations. Amplification of the DNA fragment coding for sakacin G was carried out with the aid of a “Geneamp 9700®” device (Perkin-Elmer) under the following conditions: 35 denaturing cycles at 94° C. for 30 seconds, hybridisation at 45° C. for 30 seconds and elongation at 72° C. for 1 minute, followed by an additional elongation cycle at 72° C. for 5 minutes.

[0076] The DNA fragment carrying the sakacin G locus is sequenced with the aid of an ABI Prism 310® automatic sequencer (Perkin-Elmer) using the “Big-dye terminator®” sequencing kit (Perkin-Elmer) and the appropriate nucleotide primers.

EXAMPLE 1

[0077] Isolation and Purification of Sakacin G

[0078] A 16 h culture of Lactobacillus sakei 2512 (100 ml) is centrifuged at 6000 g for 15 minutes. The culture supernatant is then heated at 70° C. for 20 minutes. The cooled supernatant is then diluted with 1 volume of water (the pH of the diluted solution must be below 6, by addition of 1M HCl if necessary) before being passed over a column (2.5×18 cm) containing a cation-exchange resin (carboxymethylcellulose; Cellufine C-200, Amicon) equilibrated with water. After washing in succession with water (100 ml) and then with a 0.1M NaCl solution (150 ml), the sakacin G is eluted with a 0.5M NaCl solution (200 ml). The pH of all the solutions must be below 6. The active fraction is then deposited on a solid-phase extraction cartridge (Sep-pak plus C18, Waters) equilibrated in water. After washing in succession with 5 ml of 20 mM ammonium acetate solutions containing 0, 10, 20 and 30% acetonitrile, the sakacin G is eluted with 10 ml of 20 mM ammonium acetate containing 80% acetonitrile. After lyophilisation, the extract is dissolved in 1 ml of 40% aqueous acetonitrile solution and then injected onto a C8 reverse phase analytical HPLC column (Kromasil, 5 μm, 100 Å, 4.6×250 mm, A.I.T.). The HPLC was carried out on an apparatus comprising a Perkin-Elmer series 200 LC pump connected to a Perkin-Elmer 785A detector. The absorption chromatogram is recorded at 220 nm. Separation is carried out, at a rate of 0.8 ml/minute, according to the following gradient: solvent A=water/0.1% trifluoroacetic acid; solvent B=acetonitrile/water/0.07% trifluoroacetic acid. After washing for 5 minutes with 20% of solvent B, elution is carried out by a gradient of from 20 to 40% of solvent B in 10 minutes then from 40 to 55% of solvent B in 20 minutes.

[0079] The fraction corresponding to the peak at 23 minutes proved to be active against Listeria ivanovii BUG 496 and was analysed by “ionspray” ionisation mass spectrometry. The molecule appears at least 95% pure and has a molecular mass of 3834.32±0.31 Da. The quantity of sakacin G so purified was estimated at 120 μg from 100 ml of culture. The purification yield was estimated at 55% of activity found. Part of the primary sequence of sakacin G was determined by microsequencing and two degenerate oligonucleotides were established starting from that sequence.

EXAMPLE 2

[0080] Cloning of the Genetic Locus Involved in the Production of Sakacin G

[0081] By reverse genetics, two degenerate oligonucleotides SakG01 (5′ AARTATTATGGNAAYGGNGT 3′) (SEQ ID No. 10) and SakG02S (5′ ACATGATGNCCNCCRTTNGC 3′) (SEQ ID No. 11) were chosen in order to amplify the DNA fragment corresponding to the structural gene of mature sakacin G (SEQ ID No. 15) by polymerase chain reaction (PCR). The amplified product so obtained, having an approximate size of 100 bp, was cloned in plasmid pGEM-T to form plasmid pJMBYC01. The restriction fragment PvuII of 560 bp, derived from pJMBYC01, including the inserted fragment, was used as the hybridisation probe during a Southern-type transfer for locating the structural gene on the genome of Lactobacillus sakei 2512. Starting from a plasmid extract of Lb. sakei 2512 digested by the restriction enzymes HindIII and EcoRI, the probe revealed fragments having sizes of approximately 2.1 and 9 kbp, respectively. The fragment HindIII of 2.1 kbp was purified and then inserted into the vector pZERO2 in order to yield the plasmid pJMBYC02. The presence of the structural gene of sakacin G in pJMBYC02 was demonstrated by PCR amplification with the primers SakG01 and SakG02 and then by nucleotide sequencing of the fragment inserted in pJMBYC02. A similar strategy was used to determine the complete sequence of the gene skgD. The plasmid extract of Lb. sakei 2512 was digested by XbaI. The digestion product was inserted into plasmid pBluescript SK+. The clones carrying the sequence of interest were revealed by means of a radioactive probe prepared by PCR carried out on plasmid pJMBYC02 with the aid of the oligonucleotides SakG03 (5′ CCTTGGTCAGGCTATCG 3′) (SEQ ID No. 16) and SakG04 (5′ ATCACCTTTTTGAATTACCC 3′) (SEQ ID No. 17).

[0082] Analysis of the complete nucleotide sequence of the region (3051 bp) revealed the existence of three complete open reading frames skgA1 and skgA2 and skgDc and a truncated frame skgI. The supposed genes skgA1, skgA2 and skgI are oriented in the opposite direction relative to skgD.

[0083] Each of the open reading frames is preceded by a potential ribosome fixing site. The genes skgA1 and skgA2 both code for proteins having 55 amino acid residues, the sequences 19-55 of which are completely identical. Sequence 19-52 corresponds to the sequence of sakacin G obtained by microsequencing. The presence of 4 cysteine residues in positions 9, 14 and 24 and in the C-terminal position is to be noted. Moreover, the calculated molecular mass of this peptide, 3838.2 Da, which differs from the measured molecular mass (3834.32 Da) by 4 Da, shows the presence of two disulfide bridges in sakacin G, as has already been demonstrated for other anti-Listeria bacteriocins.

[0084] Sequences 1-18 of the proteins SkgA1 and SkgA2 differ by only 3 residues and have strong homologies with the “leader” peptides of the class II bacteriocins, which are involved in the transport of those peptides by specific ABC transporters. In particular, the terminal GG unit is characteristic of these leader sequences and constitutes the maturation site of these bacteriocins. A comparison of the nucleotide sequences of the genes skgA1 and skgA2 also shows an identity of sequence of more than 95% for the portion of the genes coding for the mature bacteriocin.

[0085] The incomplete open reading frame called skgI codes for a protein of 52 residues. A comparison of that sequence with the database sequences shows strong homologies between SkgI and the so-called immunity proteins LccI and MesI. The involvement of MesI in protection with respect to mesentericin Y105 has been demonstrated. It may be assumed that skgI codes for the sakacin G immunity protein.

[0086] The last gene skgDc codes for a protein of 727 amino acids. According to the databases, SkgDc is highly homologous with proteins of the ABC transporter family and more especially with transporters of pediocin PA-1: PedD or PapD (Marugg et al., 1992; Appl. Environ. Microbiol. 58, 2360-2367; Motlagh et al., 1994, Lett. Appl. Microbiol. 18, 305-312), of sakacin P: SppT (Huhne et al., 1996, Microbiology 142, 1437-1448), of sakacin A: SapT (Axelsson and Holck, 1995, J. Bacteriol. 177, 2125-2137) and of mesentericin Y105: MesD (Fremaux et al., 1995, Microbiology 141, 1637-1645).

EXAMPLE 3

[0087] Inhibition Spectrum

[0088] The sakacin G sensitivity of 17 bacterial strains was tested by the well test method (see Materials and Methods). The results are shown in Table 1 below: TABLE 1 Radius of the inhibition halos (mm) Lc. lactis ATCC11454 0 Ln. Paramesenteroides DSM 20288 0 Ln. Mesenteroides DSM 20484 0 Ln. Mesenteroides DSM 20240 0 Lb. Delbrueckii DSM 20081 0 Lb. Plantarum DSM 20174 0 Lb brevis DSM 20054 0 Lb. casei DSM 20011 0 Lb. sakei 2515 1 P. acidilactici ENSAIA 583 0 P. cerevisiae IP 5492 1 E. faecium ENSAIA 631 0 E. faecalis IP 5430 2 E. faecalis ENSAIA 636 1 E. durans ENSAIA 630 2 L. inocua 8811 3 L. ivanovi BUG 496 6

[0089] The inhibition spectrum of this bacteriocin appears to be quite narrow and limited to the strains Lactobacillus sakei and Pediococcus cerevisiae for the lactic acid bacteria. Like the other class IIa bacteriocins, this peptide appears to be active against all the Listeria strains tested, as well as against Enterococcus faecalis and Enterococcus durans, but not against Enterococcus faecium.

1 17 1 196 DNA Lactobacillus sake CDS (20)..(187) 1 ttaacaggag gtattcaaa atg aag aat aca cgt agc tta acg atc caa gaa 52 Met Lys Asn Thr Arg Ser Leu Thr Ile Gln Glu 1 5 10 ata aaa tcc atc aca ggt ggt aaa tac tat ggt aat ggt gtt agc tgt 100 Ile Lys Ser Ile Thr Gly Gly Lys Tyr Tyr Gly Asn Gly Val Ser Cys 15 20 25 aac tct cat ggt tgt tca gta aat tgg ggg caa gca tgg act tgt ggg 148 Asn Ser His Gly Cys Ser Val Asn Trp Gly Gln Ala Trp Thr Cys Gly 30 35 40 2 55 PRT Lactobacillus sake 2 Met Lys Asn Thr Arg Ser Leu Thr Ile Gln Glu Ile Lys Ser Ile Thr 1 5 10 15 Gly Gly Lys Tyr Tyr Gly Asn Gly Val Ser Cys Asn Ser His Gly Cys 20 25 30 Ser Val Asn Trp Gly Gln Ala Trp Thr Cys Gly Val Asn His Leu Ala 35 40 45 Asn Gly Gly His Gly Val Cys 50 55 3 196 DNA Lactobacillus sake CDS (20)..(187) 3 4 55 PRT Lactobacillus sake 4 Met Lys Asn Ala Lys Ser Leu Thr Ile Gln Glu Met Lys Ser Ile Thr 1 5 10 15 Gly Gly Lys Tyr Tyr Gly Asn Gly Val Ser Cys Asn Ser His Gly Cys 20 25 30 Ser Val Asn Trp Gly Gln Ala Trp Thr Cys Gly Val Asn His Leu Ala 35 40 45 Asn Gly Gly His Gly Val Cys 50 55 5 181 DNA Lactobacillus sake CDS (24)..(179) 5 ttaaaaaagg agacgtgatt aaa atg gca aac aaa gac aat att aaa act gaa 53 Met Ala Asn Lys Asp Asn Ile Lys Thr Glu 1 5 10 tct aaa aac aac atc gaa gct ctc ttg cac tta cta gaa aag cgt cct 101 Ser Lys Asn Asn Ile Glu Ala Leu Leu His Leu Leu Glu Lys Arg Pro 15 20 25 gta aaa tcc agt gaa tta ctc gat att att gac gtt ctt tcc caa gtt 149 Val Lys Ser Ser Glu Leu Leu Asp Ile Ile Asp Val Leu Ser Gln Val 30 35 40 tat agc aaa att gat ata gct aag aat ccc ga 181 Tyr Ser Lys Ile Asp Ile Ala Lys Asn Pro 45 50 6 52 PRT Lactobacillus sake 6 Met Ala Asn Lys Asp Asn Ile Lys Thr Glu Ser Lys Asn Asn Ile Glu 1 5 10 15 Ala Leu Leu His Leu Leu Glu Lys Arg Pro Val Lys Ser Ser Glu Leu 20 25 30 Leu Asp Ile Ile Asp Val Leu Ser Gln Val Tyr Ser Lys Ile Asp Ile 35 40 45 Ala Lys Asn Pro 50 7 1203 DNA Lactobacillus sake CDS (20)..(1201) 7 8 394 PRT Lactobacillus sake 8 Leu Phe Asn Leu Leu Arg Tyr Lys Lys Leu Tyr Cys Ser Gln Val Asp 1 5 10 15 Glu Asp Asp Cys Gly Ile Ala Ala Leu Asn Met Ile Phe Lys Asn Phe 20 25 30 Gly Ser Glu Tyr Ser Leu Ser Lys Leu Arg Phe Leu Ala Lys Thr Ser 35 40 45 Gln Gln Gly Thr Thr Ile Phe Gly Leu Ile Lys Ala Ala Glu Glu Leu 50 55 60 Asn Leu Glu Ala Asn Ala Leu Gln Ala Asp Met Gly Ile Phe Lys Asp 65 70 75 80 Glu Asn Leu Met Leu Pro Ile Ile Ala His Val Leu Lys Gln Gly Lys 85 90 95 Val Leu His Tyr Tyr Val Val Phe Asp Val Ser Lys Asp Phe Leu Ile 100 105 110 Ile Gly Asp Pro Asp Pro Thr Ile Gly Ile Thr Glu Ile Ser Lys Lys 115 120 125 Asp Phe Glu Asn Glu Trp Thr Gly Asn Phe Ile Thr Phe Ser Lys Gly 130 135 140 Lys Asn Phe Val Ser Glu Lys Gln Arg Asn Asn Ser Leu Leu Lys Phe 145 150 155 160 Ile Pro Ile Leu Arg Gln Gln Lys Ser Leu Ile Phe Trp Ile Ala Phe 165 170 175 Ala Ala Ile Leu Leu Met Ile Ile Ser Ile Ala Gly Ser Leu Phe Leu 180 185 190 Glu Gln Leu Val Asp Ile Tyr Ile Pro His Lys Asn Met Asp Thr Leu 195 200 205 Gly Ile Ile Ser Ile Cys Leu Ile Gly Ala Tyr Leu Leu Gln Ala Val 210 215 220 Met Thr Tyr Phe Gln Asn Phe Leu Leu Thr Ile Phe Gly Gln Asn Leu 225 230 235 240 Ser Arg Lys Ile Ile Leu Asn Tyr Ile Asn His Leu Phe Glu Leu Pro 245 250 255 Met Ser Phe Phe Ser Thr Arg Arg Val Gly Glu Ile Val Ser Arg Phe 260 265 270 Thr Asp Ala Ser Lys Ile Ile Asp Ala Leu Ala Ser Thr Ile Leu Thr 275 280 285 Leu Phe Leu Asp Val Trp Met Leu Val Thr Ile Ser Ile Val Leu Val 290 295 300 Phe Leu Asn Thr Lys Leu Phe Met Ile Ser Leu Val Ser Ile Pro Val 305 310 315 320 Tyr Ser Val Ile Ile Tyr Ala Phe Lys Asn Thr Phe Asn Gly Leu Asn 325 330 335 His Lys Ser Met Glu Asn Ala Ala Leu Leu Asn Ser Ala Ile Ile Glu 340 345 350 Asn Val Thr Gly Ile Glu Thr Val Lys Ser Leu Thr Ser Glu Glu Phe 355 360 365 Ser Tyr Asn Gln Ile Thr Asp Arg Phe Glu Asn Phe Leu Asn Ser Ser 370 375 380 Leu Arg Tyr Thr Ile Ala Asp Gln Gly Gln 385 390 9 2042 DNA Lactobacillus sake 9 agcttcggga ttcttagcta tatcaatttt gctataaact tgggaaagaa cgtcaataat 60 atcgagtaat tcactggatt ttacaggacg cttttctagt aagtgcaaga gagcttcgat 120 gttgttttta gattcagttt taatattgtc tttgtttgcc attttaatca cgtctccttt 180 tttatagtaa taaaaaaaac acaattaaat tagtgctttt ttatctggta attaacaaac 240 tccatgaccg ccattagcta gatggtttac tccacaagtc catgcttgcc cccaatttac 300 tgaacagccg tgagagttac agctaacgcc attaccatag tatttaccac ctgtaataga 360 tttcatttct tgaattgtta ggctttttgc gtttttcata aagaacatct ccaaattata 420 ttttttagtg attcttgaag ttctgttgta acgcagaatt ttggaagaat gagtacttgt 480 tagaaatttg ccgatttaaa taattaacaa accccatgac cgccattagc tagatgattt 540 accccacaag tccatgcttg cccccaattt actgaacaac catgagagtt acagctaaca 600 ccattaccat agtatttacc acctgtgatg gattttattt cttggatcgt taagctacgt 660 gtattcttca ttttgaatac ctcctgttaa ataattttta cacgatcagt gtagttctaa 720 tgtgaaattg tgtcaagttt agcaaatata tattttaggc atggaaaaac ttgcttttaa 780 ttcgacttga ctataacggt ataatactgg tattactata tttgtttagc ttcacaaaaa 840 aattaggaga cttatatatt gtttaatctg ttgagataca aaaaattata ttgttcacaa 900 gtggatgaag atgattgtgg aatcgcagct ttgaatatga tttttaaaaa ttttggttcc 960 gaatattcac tatcaaaatt gcgattctta gcaaaaacca gtcaacaagg gactactatt 1020 tttggactga taaaggctgc agaggaacta aatttagaag cgaatgcatt acaagctgat 1080 atgggcatct ttaaagatga aaatttaatg ctaccaatca ttgcacatgt tttaaagcaa 1140 ggaaaagttc tgcattacta cgttgtattt gatgtttcga aagacttttt aattattggt 1200 gacccagacc caacaatagg aattacggaa atctccaaaa aggattttga aaatgaatgg 1260 acgggtaatt tcataacatt ttcaaaagga aagaactttg tttcagagaa gcagagaaat 1320 aacagtttac tcaagtttat tcctattttg agacagcaaa aatccctaat attctggata 1380 gctttcgccg caatactatt gatgataatt agtattgcag gatcactttt tttagaacaa 1440 cttgtagata tatatatacc acacaaaaat atggatacat tggggattat ctcgatttgc 1500 ttaattggag cctatctttt acaggccgta atgacgtatt ttcagaattt tttactaact 1560 atatttggac aaaatctttc tagaaaaatt attttaaatt atattaatca cctttttgaa 1620 ttacccatgt ctttcttctc aacacgtaga gttggcgaaa tagtctctcg gtttacagat 1680 gcaagcaaga ttatagatgc tttggcaagt acgattttga ctctcttttt agatgtttgg 1740 atgttggtta caatctcaat cgttctcgta tttttaaata caaagttatt tatgatttct 1800 ctggtatcta taccggtgta ctcagttata atttatgcgt ttaaaaatac atttaatggc 1860 ctgaaccata aatcaatgga aaatgcagca ttattgaatt ctgcaataat cgaaaacgta 1920 actggcatag aaactgtaaa atcattaact tcagaagaat tttcctacaa tcaaatcact 1980 gatagattcg aaaattttct taacagttcc ttacggtata cgatagctga ccaaggacag 2040 ca 2042 10 17 DNA Lactobacillus sake misc_feature 9, 15 n = A,T,C or G 10 tattatggna ayggngt 17 11 17 DNA Lactobacillus sake misc_feature 6, 9, 15 n = A,T,C or G 11 tgatgnccnc crttngc 17 12 37 PRT Lactobacillus sake 12 Lys Tyr Tyr Gly Asn Gly Val Ser Cys Asn Ser His Gly Cys Ser Val 1 5 10 15 Asn Trp Gly Gln Ala Trp Thr Cys Gly Val Asn His Leu Ala Asn Gly 20 25 30 Gly His Gly Val Cys 35 13 2214 DNA lactobacillus sake CDS (20)..(2200) 13 14 727 PRT lactobacillus sake 14 Leu Phe Asn Leu Leu Arg Tyr Lys Lys Leu Tyr Cys Ser Gln Val Asp 1 5 10 15 Glu Asp Asp Cys Gly Ile Ala Ala Leu Asn Met Ile Phe Lys Asn Phe 20 25 30 Gly Ser Glu Tyr Ser Leu Ser Lys Leu Arg Phe Leu Ala Lys Thr Ser 35 40 45 Gln Gln Gly Thr Thr Ile Phe Gly Leu Ile Lys Ala Ala Glu Glu Leu 50 55 60 Asn Leu Glu Ala Asn Ala Leu Gln Ala Asp Met Gly Ile Phe Lys Asp 65 70 75 80 Glu Asn Leu Met Leu Pro Ile Ile Ala His Val Leu Lys Gln Gly Lys 85 90 95 Val Leu His Tyr Tyr Val Val Phe Asp Val Ser Lys Asp Phe Leu Ile 100 105 110 Ile Gly Asp Pro Asp Pro Thr Ile Gly Ile Thr Glu Ile Ser Lys Lys 115 120 125 Asp Phe Glu Asn Glu Trp Thr Gly Asn Phe Ile Thr Phe Ser Lys Gly 130 135 140 Lys Asn Phe Val Ser Glu Lys Gln Arg Asn Asn Ser Leu Leu Lys Phe 145 150 155 160 Ile Pro Ile Leu Arg Gln Gln Lys Ser Leu Ile Phe Trp Ile Ala Phe 165 170 175 Ala Ala Ile Leu Leu Met Ile Ile Ser Ile Ala Gly Ser Leu Phe Leu 180 185 190 Glu Gln Leu Val Asp Ile Tyr Ile Pro His Lys Asn Met Asp Thr Leu 195 200 205 Gly Ile Ile Ser Ile Cys Leu Ile Gly Ala Tyr Leu Leu Gln Ala Val 210 215 220 Met Thr Tyr Phe Gln Asn Phe Leu Leu Thr Ile Phe Gly Gln Asn Leu 225 230 235 240 Ser Arg Lys Ile Ile Leu Asn Tyr Ile Asn His Leu Phe Glu Leu Pro 245 250 255 Met Ser Phe Phe Ser Thr Arg Arg Val Gly Glu Ile Val Ser Arg Phe 260 265 270 Thr Asp Ala Ser Lys Ile Ile Asp Ala Leu Ala Ser Thr Ile Leu Thr 275 280 285 Leu Phe Leu Asp Val Trp Met Leu Val Thr Ile Ser Ile Val Leu Val 290 295 300 Phe Leu Asn Thr Lys Leu Phe Met Ile Ser Leu Val Ser Ile Pro Val 305 310 315 320 Tyr Ser Val Ile Ile Tyr Ala Phe Lys Asn Thr Phe Asn Gly Leu Asn 325 330 335 His Lys Ser Met Glu Asn Ala Ala Leu Leu Asn Ser Ala Ile Ile Glu 340 345 350 Asn Val Thr Gly Ile Glu Thr Val Lys Ser Leu Thr Ser Glu Glu Phe 355 360 365 Ser Tyr Asn Gln Ile Thr Asp Arg Phe Glu Asn Phe Leu Asn Ser Ser 370 375 380 Leu Arg Tyr Thr Ile Ala Asp Gln Gly Gln Gln Ala Leu Lys Val Gly 385 390 395 400 Leu Lys Leu Ile Leu Ile Val Phe Ile Leu Trp Ala Gly Ala Ile Gln 405 410 415 Val Met Arg Gly Asn Leu Thr Val Gly Arg Leu Leu Ala Phe Asn Ala 420 425 430 Leu Val Thr Tyr Phe Leu Asn Pro Leu Glu Asn Ile Ile Asn Leu Gln 435 440 445 Pro Lys Leu Gln Thr Ala Arg Val Ala Asn Ile Arg Leu Asn Glu Val 450 455 460 Leu Leu Val Asp Ser Glu Phe Asn Arg Gly Gly Arg Asp Ser Ser Thr 465 470 475 480 Asn Leu Asn Gly Asp Ile Val Phe Gln Asp Val Glu Phe Ser Tyr Gly 485 490 495 Tyr Gly Ser Asn Val Leu His Asn Ile Asn Ile Lys Ile Gln Lys Asn 500 505 510 Ser Ser Thr Thr Ile Val Gly Met Ser Gly Ser Gly Lys Ser Thr Leu 515 520 525 Ala Lys Leu Met Val Gly Phe Tyr Gln Ala Gly Ser Gly Gln Ile Leu 530 535 540 Leu Asn Gly Lys Leu Ile Asp Asn Ile Asp Arg His Ala Leu Arg Gln 545 550 555 560 Ser Ile Thr Tyr Val Pro Gln Glu Pro Val Met Phe Ala Gly Thr Ile 565 570 575 Leu Glu Asn Leu Ile Met Gln Asn Lys Arg Asn Leu Ser Ile Asp Lys 580 585 590 Val Lys Glu Ala Cys Arg Ile Ala Glu Ile Asp Lys Asp Ile Glu Asn 595 600 605 Phe Pro Met Gly Tyr Asp Thr Asp Ile Ser Glu His Gly Ser Ser Ile 610 615 620 Ser Val Gly Gln Lys Gln Arg Leu Ser Ile Ala Arg Ser Leu Leu Thr 625 630 635 640 Glu Ser Asn Val Leu Leu Phe Asp Glu Ser Thr Ser Ser Leu Asp Thr 645 650 655 Ile Thr Glu Gln Arg Ile Ile Glu Asn Leu Leu Asn Leu Asn Asp Lys 660 665 670 Thr Leu Ile Phe Val Ala His Arg Leu Ser Val Ala Lys Gln Thr Glu 675 680 685 Asn Ile Ile Val Met Asp His Gly Gly Ile Val Glu Thr Gly Ser His 690 695 700 Asp Lys Leu Ile Leu Glu Asn Gly Tyr Tyr Lys Glu Leu Cys Thr Val 705 710 715 720 Lys Thr Lys Lys Lys Glu Phe 725 15 3055 DNA lactobacillus sake 15 agcttcggga ttcttagcta tatcaatttt gctataaact tgggaaagaa cgtcaataat 60 atcgagtaat tcactggatt ttacaggacg cttttctagt aagtgcaaga gagcttcgat 120 gttgttttta gattcagttt taatattgtc tttgtttgcc attttaatca cgtctccttt 180 tttatagtaa taaaaaaaac acaattaaat tagtgctttt ttatctggta attaacaaac 240 tccatgaccg ccattagcta gatggtttac tccacaagtc catgcttgcc cccaatttac 300 tgaacagccg tgagagttac agctaacgcc attaccatag tatttaccac ctgtaataga 360 tttcatttct tgaattgtta ggctttttgc gtttttcata aagaacatct ccaaattata 420 ttttttagtg attcttgaag ttctgttgta acgcagaatt ttggaagaat gagtacttgt 480 tagaaatttg ccgatttaaa taattaacaa accccatgac cgccattagc tagatgattt 540 accccacaag tccatgcttg cccccaattt actgaacaac catgagagtt acagctaaca 600 ccattaccat agtatttacc acctgtgatg gattttattt cttggatcgt taagctacgt 660 gtattcttca ttttgaatac ctcctgttaa ataattttta cacgatcagt gtagttctaa 720 tgtgaaattg tgtcaagttt agcaaatata tattttaggc atggaaaaac ttgcttttaa 780 ttcgacttga ctataacggt ataatactgg tattactata tttgtttagc ttcacaaaaa 840 aattaggaga cttatatatt gtttaatctg ttgagataca aaaaattata ttgttcacaa 900 gtggatgaag atgattgtgg aatcgcagct ttgaatatga tttttaaaaa ttttggttcc 960 gaatattcac tatcaaaatt gcgattctta gcaaaaacca gtcaacaagg gactactatt 1020 tttggactga taaaggctgc agaggaacta aatttagaag cgaatgcatt acaagctgat 1080 atgggcatct ttaaagatga aaatttaatg ctaccaatca ttgcacatgt tttaaagcaa 1140 ggaaaagttc tgcattacta cgttgtattt gatgtttcga aagacttttt aattattggt 1200 gacccagacc caacaatagg aattacggaa atctccaaaa aggattttga aaatgaatgg 1260 acgggtaatt tcataacatt ttcaaaagga aagaactttg tttcagagaa gcagagaaat 1320 aacagtttac tcaagtttat tcctattttg agacagcaaa aatccctaat attctggata 1380 gctttcgccg caatactatt gatgataatt agtattgcag gatcactttt tttagaacaa 1440 cttgtagata tatatatacc acacaaaaat atggatacat tggggattat ctcgatttgc 1500 ttaattggag cctatctttt acaggccgta atgacgtatt ttcagaattt tttactaact 1560 atatttggac aaaatctttc tagaaaaatt attttaaatt atattaatca cctttttgaa 1620 ttacccatgt ctttcttctc aacacgtaga gttggcgaaa tagtctctcg gtttacagat 1680 gcaagcaaga ttatagatgc tttggcaagt acgattttga ctctcttttt agatgtttgg 1740 atgttggtta caatctcaat cgttctcgta tttttaaata caaagttatt tatgatttct 1800 ctggtatcta taccggtgta ctcagttata atttatgcgt ttaaaaatac atttaatggc 1860 ctgaaccata aatcaatgga aaatgcagca ttattgaatt ctgcaataat cgaaaacgta 1920 actggcatag aaactgtaaa atcattaact tcagaagaat tttcctacaa tcaaatcact 1980 gatagattcg aaaattttct taacagttcc ttacggtata cgatagctga ccaaggacag 2040 caagctttaa aagtgggttt gaagctaatt cttatagtct ttatcttatg ggctggagca 2100 atccaagtta tgagggggaa tctcacagtc ggaagattat tggcttttaa tgctttagta 2160 acatactttt taaatccctt agagaatatt attaatttac aaccaaagct acaaactgca 2220 agagtcgcta atattagact aaatgaagta ttattagtgg attctgagtt taataggggg 2280 ggacgcgaca gctcaacaaa cttaaatggg gatatcgtat ttcaagatgt agaatttagt 2340 tatggttacg gatcgaacgt attgcacaac atcaatataa aaatacaaaa gaatagtagt 2400 acaacgattg ttggtatgag cggttctggg aaatccacat tagcaaaatt aatggttggt 2460 ttctatcaag ccggatcagg acaaatatta ttaaatggta aattaatcga taacattgat 2520 cgtcatgccc tgagacaatc gattacgtat gtaccacagg aaccggtaat gttcgcaggt 2580 acaattttag aaaatcttat tatgcagaat aaaagaaatt tatctattga taaagtgaaa 2640 gaggcatgta ggatagccga aattgataaa gatatagaaa attttcctat ggggtatgat 2700 acagatattt ccgaacatgg gagttcaatc tcagtaggtc aaaaacaaag actttctatt 2760 gcaagatcac tgctgacaga gtctaatgtt ttactgtttg atgaatcaac cagtagtttg 2820 gacactatta ctgagcagcg aataattgaa aacctattga atttaaatga caaaacatta 2880 atattcgttg cacatcgatt gtcagttgct aagcaaactg aaaatattat cgttatggat 2940 cacggtggaa ttgttgaaac aggttcgcat gataaattaa tattggaaaa tggatattat 3000 aaagaattat gtactgtgaa gacgaagaaa aaagaatttt agataaaaca aaaac 3055 16 17 DNA lactobacillus sake 16 ccttggtcag gctatcg 17 17 20 DNA lactobacillus sake 17 atcacctttt tgaattaccc 20 

1. Isolated polypeptide, characterised in that it is a bacteriocin, named sakacin G, derived from Lactobacillus sakei
 2512. 2. Isolated polypeptide according to claim 1, characterised in that it is a class IIa bacteriocin.
 3. Isolated polypeptide, characterised in that it comprises sequence ID No. 2 and/or sequence ID No.
 4. 4. Isolated polypeptide, characterised in that it comprises sequence ID No.
 12. 5. Nucleic acid comprising a nucleotide sequence coding for a polypeptide according to any one of claims 1 to
 4. 6. Nucleic acid according to claim 5, comprising sequence ID No. 1 and/or sequence ID No.
 3. 7. Nucleic acid according to claim 5 or 6, comprising the nucleic acid sequence SEQ ID No.
 15. 8. Nucleic acid according to claim 5 or 6, comprising the nucleic acid sequence SEQ ID No.
 9. 9. Isolated polypeptide, characterised in that it comprises sequence ID No.
 6. 10. Isolated polypeptide, characterised in that it comprises sequence ID No.
 8. 11. Isolated polypeptide, characterised in that it comprises sequence ID No.
 14. 12. Nucleic acid comprising sequence ID No.
 5. 13. Nucleic acid comprising sequence ID No.
 7. 14. Nucleic acid comprising sequence ID No.
 13. 15. Cloning and/or expression vector comprising a nucleic acid according to any one of claims 5 to 8, 12 or
 14. 16. Host cell transformed by a vector according to claim
 15. 17. Host cell according to claim 16, characterised in that it is a microorganism selected from the groups Lactococcus, Lactobacillus, Leuconostoc, Streptococcus, Pediococcus, Escherichia, or it is a yeast.
 18. Process for the production of a recombinant polypeptide, in which a vector comprising a nucleic acid according to any one of claims 5 to 8 and 12 or 14 is transferred into a host cell which is cultured under conditions permitting the expression of a polypeptide according to any one of claims 1 to 4 and 9 to 11 or of a polypeptide coded for by a nucleic acid sequence as defined in any one of claims 5 to 8 and 12 or
 14. 19. Use of a polypeptide according to any one of claims 1 to 4 as an active agent against pathogenic or undesirable flora in the preparation of food products.
 20. Use according to claim 19, characterised in that said polypeptide is used to inhibit the growth and propagation of Listeria, more especially of Listeria monocytogenes, in food products.
 21. Use according to claim 19 or 20, characterised in that said polypeptide is produced in the food product from the strain Lactobacillus sakei
 2512. 22. Use of the strain Lactobacillus sakei 2512 in food products to produce therein a bacteriocin polypeptide according to any one of claims 1 to
 4. 23. Bacteriocin composition, characterised in that it comprises at least one polypeptide according to any one of claims 1 to 4 or the strain Lactobacillus sakei
 2512. 